Glass used in buildings and vehicles protects in general from environment such as rain, wind, noise, and keeps ambient temperature within buildings or houses etc., allowing more pleasant indoor conditions. However, ordinary glass does not protect from solar radiation, since it only absorbs a part of the UV radiation, reflecting a total of about 7% and transmitting much of the solar spectrum.
Solar control refers to the ability to change the amount of transmitted or reflected solar radiation, in the near ultraviolet spectral ranges (UV; 300-380 nm), visible (VIS; 380-780 nm) and infrared (IR; 780-2500 nm). Low transmittance is generally pursued in UV and IR ranges, while the VIS transmittance may be high (>70%) or low, depending on application.
There are many choices for obtaining solar control properties to reduce energy transmittance through glass and the properties of absorption and reflection of glass sheets.
At present there are a number of blue glass types for the construction or automotive industry, based on a composition of soda-lime-silica glass.
The blue color can be obtained with iron only, by changing the balance to relatively high Redox values, close to 50%; unlike this production method, vacuum is avoided for refining, that is, the same standard cast-refining process is used as in the manufacture of commercial green, gray, bronze and clear solar control glass.
There exist developments for blue colored glasses, for example U.S. Pat. No. 5,070,048 refers to a blue glass components comprising a soda-lime-silica conventional base glass and specific amounts of Fe2O3, Co3O4, NiO, and optionally Se, resulting in an illuminant C transmittance of 54%+/−3% for a quarter inch thickness, dominant wavelength of 482 nm+/−0.1 nm, and a color purity of 13%+/−0.1%.
The U.S. Pat. No. 6,313,053 relates to a blue glass composition that absorbs infrared and ultraviolet radiation having a composition of soda-lime-silica based glass and additionally iron and cobalt, and optionally chromium, as materials absorbing solar radiation and colorants. In particular, blue colored glass includes about 0.40 to 1.0% by weight total iron, preferably about 0.50 to 0.75% by weight, about 4 to 40 ppm CoO, preferably 4 to 20 ppm, and 0 to 100 ppm Cr2O3. The redox ratio for the glass of the present invention is greater than 0.35 to about 0.60, and preferably between about 0.36 to 0.50. In a particular embodiment of the invention, the glass has a luminous transmittance of at least 55% and a color characterized by a dominant wavelength of 485-489 nanometers and a purity of about 3 to 18 percent. In another embodiment of the invention, the glass has a luminous transmittance of at least 65% in a thickness of about 0.154 inch (3.9 mm) and a color characterized by a dominant wavelength of 485-492 nanometers and a purity of about 3 to 18 percent.
The U.S. Pat. No. 6,995,102 relates to a blue glass composition comprising a soda-lime-silica based composition and a colorant portion consisting essentially of about 0.4 to 0.65 weight percent total iron oxide, about 0.1 to 0.3 weight percent manganese oxide, and cobalt oxide in an amount effective for producing a cobalt concentration of 0.0002 to 0.00013% by weight (about 2 to 13 ppm). The glass is characterized by a ratio of ferrous oxide to total iron oxide between about 0.43 and 0.58. The glass composition has a combination of high visible transmittance, high infrared absorption and an improved blue coloration. This is largely attributed to the combination of iron oxide and cobalt oxide and to the manganese oxide effect in reducing the formation of iron sulfide, thereby preventing the amber coloration.
U.S. Pat. No. 7,670,977 relates to a glass composition of the soda-lime-silica type comprising blue coloring agents in an amount varying within the following limits by weight: TABLE-US-00001 Fe2O3 (total iron) 0.2 to 0.51%, CoO 10 to 50 ppm, Cr2O3 10 to 300 ppm, CuO 0-400 ppm, the glass exhibits a redox factor less than 0.35, a Lambda.sub.D dominant wavelength between 485 and 489 nm, less than 13% purity and selectivity at least equal to 1.1 for a thickness of between 3 and 5 mm. It also relates to a glass sheet obtained from the above composition, said sheet is intended in particular to form an automotive or construction industry window.
The U.S. Pat. No. 8,187,988 relates to a blue glass composition for manufacturing windows, using a soda-lime-silica type base glass composition comprising blue coloring agents as mentioned below in an amount varying within the following limits by weight: TABLE-US-00001 Fe2O3 (total iron) from 0.2 to 0.51%; CoO 10 to 50 ppm; Cr2O3 10 to 300 ppm; CuO 0-400 ppm, glass presenting a redox factor less than 0.35, a dominant wavelength (λ) SUB.D between 485 and 489 nm, an excitation purity of at least 13%, and a selectivity at least equal to 1.1 for a thickness of between 3 and 5 mm. It also relates to a glass sheet obtained from the above composition, said sheet being intended in particular to form an automotive or construction industry window.
Furthermore, it is well known by those skilled in the art, that the addition or substitution of one or more dyes instead of other or others, or changing the proportional amount relative to the glass composition, affects not only the product color, such as the dominant wavelength or color excitation purity, but also the luminous transmission, the heat absorption and additional properties such as the transmittance of ultraviolet and infrared radiation.
For example, iron is present in (soda-lime-silica) glass in two oxidation states: as ferrous oxide (FeO) and ferric oxide (Fe2O3). Each state of oxidation-reduction confers different properties; the ferrous ion has a broad and strong absorption band centered at 1050 nm, which results in a decrease of infrared radiation. Furthermore, this band extends to the visible region decreasing light transmittance and imparting a bluish coloration to glass; on the other hand, the ferric ion has a strong absorption band located in the ultraviolet region which prevents the transmission of ultraviolet radiation through the glass and two weak bands in the visible region located between 420 and 440 nm, which causes a slight decrease of light transmittance and yellowing in the glass.
The balance between ferrous and ferric oxide has a direct effect on the color and transmittance properties of the glass.
            %      ⁢                          ⁢                        Fe                      +            2                          ⁡                  (          Ferrous          )                      =                  FeO        ×        100                              Fe          2                ⁢                  O          3                ⁢                                  ⁢        Total                        %      ⁢                          ⁢                        Fe                      +            3                          ⁡                  (          Ferric          )                      =                            Fe          2                ⁢                  O          3                ×        100                              Fe          2                ⁢                  O          3                ⁢                                  ⁢        Total            
This means that the higher the amount of ferric iron (Fe+3) present in the glass, the greater the absorption of ultraviolet radiation and light transmittance will increase; as well as the yellowish hue; but, if the content of ferrous iron (Fe+2) increases as a result of chemical reduction of Fe2O3, the absorption of infrared radiation increases, but the absorption of ultraviolet radiation decreases and also the light transmission (undesirable).Fe3+(yellow)⇄Fe2+(blue)[yellow+blue=green]2Fe2O3⇄4FeO+O2 
Varying the concentration of FeO in relation to Fe2O3 results in a change of color in the glass. The shift in hue can be changed from yellow (less Tuv, greater TL and Ts) through green, blue till reaching amber. Color changes as follows (experimental results)
Yellow—Low ferrous (12%)—High light transmission (high ferric ion)
Greenish yellow (16%)
Yellowish green (20%)
Green (25% typical green glass value)
Bluish green (29%)
Greenish blue (35%)
Blue (50%)
Olive green (60%)
Champagne (65%)
Amber—High ferrous (75%)—Low light transmission (low ferric ion)
In order to control the balance between ferrous and ferric oxide necessary to achieve solar control glass, it is necessary to establish the conditions; in mix and melting atmosphere; for the first case, the concentration of reducing agents such as coal and oxidant agents such as sodium sulfate and sodium nitrate is adjusted. As for melting conditions, it is necessary to adjust the atmosphere with varying oxygen content; depending on the thermal performance and the desired glass hue.
Titanium Oxide (TiO2) in Soda-Lime-Silica Glasses
The most stable titanium form in glasses is the tetravalent (Ti4+) form. The trivalent form may confer coloration, however this effect is not found in soda-lime-silica glass. The document “Effects of titanium dioxide in glass” by MD Beals, The Glass Industry, September, 1963, pp 495-531, describes the interest in titanium dioxide as a glass component. The effects of the use of titanium dioxide include comments about TiO2 greatly increasing the refractive index, increasing light absorption in the ultraviolet region, and reducing viscosity and surface tension. From data on the use of titanium dioxide in enamel, it was found that TiO2 increases chemical durability and acts as a flux. In general, clear glasses containing titanium dioxide can be found in all common glass formation systems (borates, silicates and phosphates). The different regions of glass formation for systems containing titanium dioxide are not grouped in a single place, since the organization of the discussion is based more on the properties of glasses containing titanium dioxide rather than their own constitution.
Moreover, addition of selenium to soda-lime-silica glass can produce a pink color due to the presence of atomic selenium. Selenium is one of the more to widely used, physical bleaching agents for glasses containing iron traces due to undesirable impurity in the raw materials, since its coloration neutralizes ferrous and ferric ions present in the glass.
The combination of iron and selenium in soda-lime-silica glass imparts a reddish-brown color and a decrease in light transmission due to an absorption band located in the visible region between 490 and 500 nm (similar to the atomic selenium band). This band extends into the ultraviolet region, causing also a decrease of transmittance in this type of glass.
The intensity of staining and the final properties of the glass are based on the concentration of iron oxide and selenium in glass.
For concentrations higher than 0.1% Fe2O3 it is necessary to use selenium together with small amounts of cobalt oxide <0.0001% since it best compensates the hue resulting from the iron contents; these mixtures achieve the neutral tone, however, there is an alteration in visible transmittance.
The copper oxide is incorporated as a key element in developing turquoise blue color necessary to adjust or compensate the yellowing that could develop as a result of incorporation of titanium dioxide and chromium oxide.
It is well known that copper has played an important part in the production of glass, ceramics and colored pigments. For example, the coloration of the Persian ceramics has been recognized for its tonality conferred by copper. Of special interest for ceramic artists are the turquoise blue and especially the Egyptian and Persian dark blue colors (Waldemar A. Weil; Colored Glasses, Society of Glass Technology, Great Britain, P. 154-167, 1976).
Copper has been used in glass compositions, not only in those of soda-lime-silica type, but in some others, such as those containing borosilicate, for example. Therefore, the developed color depends on the base glass, on its concentration and its oxidation state.
In the case of a soda-lime-silica type base glass, copper in oxide form imparts a coloration of a greenish blue hue, specifically turquoise, however, in glass, copper can be in its monovalent state, which does not impart any color. So, the greenish blue coloration depends not only on the amount of copper present, but on the ionic balance between the cuprous and cupric states. The maximum absorption of copper oxide is in a band centered at 780 ηm and a weak secondary peak is present at 450 ηm, which disappears at high soda content (about 40% by weight) (C. R. Bamford, Colour Generation and Control in Glass, Glass Science and Technlogy, Elsevier Scientific Publishing Company, P. 48-50, Amsterdam, 1977).
Although the above described glasses are acceptable for some applications, what is sought is values of visible light transmittance (TL) greater than 50% when the glass is used in the construction industry and the thickness may reach up to 12 mm; on the other hand, when the glass is used in automotive windows and windshields, transmittal values should be greater than 70%.
The present invention provides good control of solar transmission, due to the incorporation of iron oxide (Fe2O3), and shows a reduction of UV radiation due to the incorporation of titanium dioxide (TiO2) and small amounts of selenium (Se). Likewise, chromium oxide (Cr2O3) can be optionally incorporated to increase this value. Aqua blue coloration is obtained by combinations of iron oxide (Fe2O3) And cobalt oxide (CO3O4).
The addition of copper oxide (CuO) in combination with iron oxide, cobalt oxide, selenium and titanium oxide is used as an alternative for obtaining a blue hue for use in the automotive or construction industry, which has a light is transmission (TLA), illuminant “A” greater than 50%, a dominant wavelength (λ) of 487 nm to 498 nm, and an excitation purity of less than 12 for glass thickness between 3 and 12 mm.
It has been found that in industrial production adding CuO in concentrations below 120 ppm is feasible for a thickness of 4 mm, and less than 100 ppm for a thickness of 6.0 mm
The glass can also be manufactured in smaller thicknesses such as glass used in the manufacture of windshields. If higher concentrations of CuO are present during formation within the float bath, a process of reduction attributable to the process atmosphere could occur, causing a reddish color in the glass surface, which can be observed as a reflection. This effect is related to the residence time and the speed of advance of the glass ribbon, which means that at lower speeds, it is necessary to reduce the content of CuO in glass.
As seen from the above, the present invention has the advantage that it can be used both in the construction industry and in the automotive industry, since the values of visible light transmittance (TL) are greater than 50% when glass is used in the construction industry and thickness may reach up to 12 mm; on the other hand, when the glass is used in windows and automotive windshields, transmittal values should be greater than 70%.